When I was a kid and I asked my mom how you can tell boy and girl babies apart, she told me that "boy's insides were on their outsides". I took it literally to mean that boys had all their guts hanging out of them.
A childhood belief about rude bits

others believed things like this
- I used to believe that boys had boy babies, and girls had girl babies.
That was when I was 3-7. I'm 15 now.— Stefanie Michelle - My neighbor girl told me that "crazy men can have babies"— Russ
- My neighbor told me that the insides of acorns tasted like chocolate. They don't. They're really bitter.— Dial Zero
- I never knew why boys had to lift up the toilet seat...until my friend told me that boys had bad aim.Anon
- When i was younger i believed that a cat was a girl and dogs were boys.Anon
- When I was a little girl, I believed that all cats were girls and all dogs were boys. :)— Mary Ellen